Systems and Methods for Performing Spine Surgery

ABSTRACT

This application describes surgical instruments and implants for building a posterior fixation construct across one or more segments of the spinal column during a medialized posterior lumbar interbody fusion (PLIF) procedure.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/160,988, filed on Oct. 15, 2018, now pending, which is a continuationof U.S. patent application Ser. No. 15/586,059, filed on May 3, 2017,now U.S. Pat. No. 10,098,625, which is a continuation of U.S. patentapplication Ser. No. 15/202,464, filed on Jul. 5, 2016, now U.S. Pat.No. 9,649,099, which is a continuation of U.S. patent application Ser.No. 14/794,709, filed on Jul. 8, 2015, now U.S. Pat. No. 9,386,971,which is a continuation of U.S. patent application Ser. No. 13/601,986,filed on Aug. 31, 2012, now U.S. Pat. No. 9,113,853, which claims thebenefit of priority under 35 U.S.C. 119(e) from U.S. Provisional PatentApplication No. 61/529,495, filed on Aug. 31, 2011, now expired, andentitled “Tissue Retraction Assembly and Related Methods,” the entirecontents of which are each hereby expressly incorporated by referenceinto this disclosure as if set forth fully herein.

FIELD

This application describes surgical instruments and implants forperforming minimally invasive posterior fusion across one or moresegments of the spinal column.

BACKGROUND

Posterior Lumbar Interbody Fusion (PLIF) involves access theintervertebral disc space from a posterior approach, removing bone anddisc material, and positioning one or more intervertebral implants intothe disc space. Additional fixation hardware in the form of pediclescrews and rods are also generally applied to stabilize the spine inposition until fusion occurs through the disc space. The pedicle screwsare advanced into the vertebral body through the pedicle starting at theintersection of the transverse process and the inferior articulatingprocess of the superior facet. Typical trajectories between pediclescrews within the same vertebral body converge and the trajectory isalso often directed inferiorly. Thus, in order to accommodate theimplantation of the fixation hardware the traditional PLIF exposurerequires exposure out to transverse process which includes stripping ofmusculature and associated morbidity.

The instruments, tools, and techniques described herein are directedtowards reducing the exposure required to perform an instrumented PLIFand other challenges associated with PLIF procedures.

SUMMARY OF THE INVENTION

The present application describes a medialized PLIF exposure. Themedialized exposure can be made much smaller than the traditionalexposure. Exposure does not require stripping of musculature all the wayout to the transverse process. Exposure generally opens out only to thefacet joints on the lateral margin. Screws are still advanced into thevertebral body through the pedicle, however, starting point is moremedial and slightly inferior. The starting point is typically justmedial and inferior to the articulating surface of the superior facet.

The retractor is designed for use during spinal surgery, andparticularly for a medialized PLIF (posterior interbody fusion) surgery.The retractor moves and maintains tissue out of the area between theretractor blades to provide access to the spine. The narrow blades maybe advanced to the spine first with the use of an attachment handle. Theconnectors on each side of the retractor may then be attached to therespective connection post on the blades and the handles can be removed.The retractor has a dual translating rack (as opposed to a single armthat moves in relation to a fixed arm). This permits the pressuredistribution to be equal on both sides of the access corridor when beingopened, such that the center of the access corridor doesn't shift duringopening. The retractor body may be attached to an articulating arm(A-arm), which is turn is attached to the bedrail to fix the position ofthe retractor.

The blades attach to the retractor body at the open receptacles. Theengagement latch inside the open receptacle moves freely on its own sothat it will be pressed inside the locking arm when the blade is beinginserted and will be spring loaded back into locking position once theblade is fully inserted. To release the blade from the retractor, therelease button is pressed which will cause the engagement latch to moveback into the locking arm so that the blade can slide out. When therelease button is released, torsion springs force the release button andengagement latch back into their locked position.

The two-tiered connection post allows the retractor blades to beattached to the retractor body without (or before) removing theattachment handle from the blade, or, one of the blades fixed relativeto the table (via an A-arm) prior to attaching the retractor body to theblade. The connection posts of the blades also permit rotation of theblades about the axis of the notch receptacle such that the blades selfalign and reduce pressure points on the retracted tissue. The connectionpost is fixed relative to the blade by the connection nut making it sothat the blade cannot rotate around the connection post. Instead, theblade rotates via the engagement between the connection post and thelocking arm. The open receptacle of the locking arm securely surroundsthe lower tier of the connection post, but the connection post is freeto rotate inside the open receptacle 360 degrees.

Friction mechanisms are provided to create friction between the pivotpiece and the track connector and the pivot piece and locking arm. Thisprevents the retractor arms from flopping around. A release button isprovided on the locking arm of the moving arm so that the blades can bereleased from the retractor. Pressing the release button will move theengagement latch backwards and the blades can then slide out. When therelease button is released, torsion springs force the release button andengagement latch back into their locked position. The engagement latchmoves into the arm independent of the release button such that therelease button does not move when the blades are inserted.

The thumb tab of the locking mechanism is connected to a pinion shaft soit can be pulled to an upright position. Once in the upright positionthe thumb tab can be rotated which adjusts the retractor and theoperative corridor created by it. This retractor has a dual translatingrack so that both arms of the retractor move instead of just one arm.This is advantageous because it prevents slipping of the retractor armthat often occurs with retractors having a fixed arm because of thepressure differences between the two arms. With this retractor, thepressure on both arms is equal so neither arm will slip, providing amore predictable access corridor. The adjustment mechanism includes apawl so that the racks can only move in one direction at a time. Whenthe desired access has been achieved, the surgeon can rotate the pawlthat will lock the thumb tab in place. This is advantageous since itwill insure that the thumb tab is not accidently rotated during surgerythat would cause the retractor to open up more than necessary. A ballplunger holds the pawl open when one wishes to close the retractor. Thisprevents the user from having to hold the pawl open while closing theleft and right arms.

A bone anchor provided is configured for use with the tissue retractorduring a medialized PLIF procedure according to one embodiment. By wayof example only, the bone anchor includes a tulip and a shank. The tulipis configured to be coupled to the shank in situ if desired, that is,after the shank has been anchored into the pedicle. The tulip isconfigured to lockingly receive a spinal rod. The shank comprises athread configuration tailored to the typical bone pattern along themedialized trajectory followed. By way of example only, the shankcomprises three different thread zones.

An interbody implant according to one example embodiment is alsodescribed. The interbody implant is designed for bilateral placementalong the apophyseal ring at each lateral aspect of the disc space. Theimplant is also configured to be reversible, that is, a single implantconfiguration can be utilized as either the left implant or rightimplant (when positioned bilaterally). The implant is also configured tobe inserted via either impaction or insert and rotate techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a top view of a minimally invasive surgical exposure createdby one example of a tissue retraction system in use during a posteriorlumbar interbody fusion (PLIF) procedure according to one exampleembodiment;

FIGS. 2 and 3 are perspective and side views, respectively, of thetissue retraction system of FIG. 1;

FIG. 4 is a perspective view of the retractor forming part of the tissueretraction system of FIG. 2;

FIG. 5 is a sectional view of the retractor of FIG. 2;

FIGS. 6-11 are various views of a right retractor blade forming part ofthe tissue retraction system of FIG. 2;

FIGS. 12-17 are various views of a left retractor blade forming part ofthe tissue retraction system of FIG. 2;

FIGS. 18-23 are various views of a narrow left retractor blade formingpart of the tissue retraction system of FIG. 2;

FIG. 24 is a perspective view of one example of a blade holder formingpart of the tissue retraction system of FIG. 2;

FIGS. 25 and 26 are perspective and side views, respectively, of theblade holder of FIG. 24 coupled with the right retractor blade of FIG.6;

FIG. 27 is a side sectional view of the blade holder and right retractorblade combination of FIG. 25;

FIGS. 28 and 29 are perspective and exploded perspective views,respectively, of an example of a bone screw suitable for use in the PLIFprocedure of FIG. 1;

FIG. 30 is a side view of a screw shank forming part of the bone screwof FIG. 28;

FIGS. 31 and 32 are perspective views of an example of an interbodyimplant suitable for use during the PLIF procedure of FIG. 1;

FIGS. 33 and 34 are plan views of the leading and trailing ends,respectively, of the interbody implant of FIG. 31;

FIGS. 35 and 36 are plan views of the lateral sides of the interbodyimplant of FIG. 31;

FIGS. 37 and 38 are plan views of the vertebral engaging sides of theinterbody implant of FIG. 31; and

FIGS. 39-48 illustrate various steps in the minimally invasive PLIFprocedure of FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The system and method for performing spine surgerydisclosed herein boasts a variety of inventive features and componentsthat warrant patent protection, both individually and in combination.

The present application describes a system for performing posteriorlumbar interbody fusion (PLIF) surgery. Referring to FIG. 1, the PLIFsystem includes a tissue retractor 10, a plurality of bone anchors 12,at least one spinal rod 14, and at least one interbody implant 16. Thetissue retractor 10 is used to establish and maintain an operativecorridor to the surgical target site. Once this access has beenestablished, the bone anchors 12 may be implanted into the vertebralbodies, the disc space and vertebral endplates may be prepared, one ormore interbody implants 16 may be inserted into the disc space, andspinal rods 14 may then be used to align and compress the construct.

Referring to FIGS. 2-5, the tissue retractor 10 includes an accessdriver body 20, first and second racks 22, 24, and right and left arms26, 28. Right and left retractor blades 30, 32 are removably attached tothe right and left arms 26, 28, respectively. In use during a PLIFprocedure described herein, it is important that the tissue retractor 10be positioned relative to the patient such that the access driver body20 is located above (i.e. cranially of) the wound and in the middle ofthe patient's back (e.g. directly over the spinal column). This willensure that the various beneficial features of the tissue retractor 10described herein are fully utilized. Furthermore, all orientationreferences herein to “right” and “left” are to be interpreted asrelative to the patient. Thus, the right retractor blade 30 will alwaysbe positioned within the surgical wound near the patient's right side,and the left retractor blade 32 will always be positioned within thesurgical wound near the patient's left side. As will be explained below,this orientation is necessary because the right and left retractorblades are asymmetric in shape and therefore are not interchangeable.

The access driver body 20 has first and second channels 34, 36 extendinglaterally through the body. The first and second channels 34, 36 aresized and dimensioned to receive the first and second racks 22, 24respectively therein, and are separated from one another by a distancesufficient to enable placement of a pinion 44 to control translation ofthe racks 22, 24 as described below. A thumb tab 38 is rotatable tocontrol the directional translation of the racks 22, 24. By way ofexample only, rotating the thumb tab in a clockwise directionsimultaneously causes the first rack 22 to translate toward the rightside and the second rack 24 to translation toward the left side. Thistranslation in turn causes the retractor blades 30, 32 to move in thesame direction as the racks, controlling the size of the surgical wound.A pawl 40, moveable from a first (e.g. “unlocked”) position to a second(e.g. “locked”) position is provided to enable locking of the retractor10 in an open position during use. The pawl 40 includes a wedge 42 (FIG.5) that is configured to engage the teeth 48 of the second rack 24 anddirectly prevent translation of the second rack 24 when the pawl 40 isin the second “locked” position. This also indirectly preventstranslation of the first rack 22, effectively locking the retractor 10in an “open” configuration. When the pawl 40 is in the first “unlocked”position, the wedge 42 is disengaged from the teeth 48, allowing freetranslation of the racks 22, 24. A pinion 44 is positioned between theracks 22, 24 and is mechanically coupled with the thumb tab 38 such thatturning the thumb tab 38 causes the pinion 44 to rotate, which in turncauses the racks 22, 24 to translate. The access driver body furtherincludes an articulating arm attachment 46 to enable attachment to anarticulating arm during use.

By way of example only, the racks 22, 24 are generally rectangularelongated members having a plurality of teeth 48 distributed on one sideof each of the racks 22, 24. The teeth 48 are configured to interactwith the pinion 44 described above to allow controlled translation ofthe arms 26, 28.

The right arm 26 includes a proximal segment 50, a middle segment 52,and a distal segment 54. The proximal segment 50 includes a firstaperture 56 and a second aperture 58. The first aperture 56 isconfigured to fixedly receive the first rack 22 such that the first rack22 and proximal segment 50 are generally perpendicular to one another.Thus, translation of the first rack 22 in either direction causes acorresponding movement of the right arm 26 in the same direction. Thesecond aperture 58 is configured to slidingly receive the second rack 24therethrough such that the second rack 24 is able to pass through theproximal segment 50 unencumbered in either direction during translation.The proximal segment 50 further includes a pivot member 60 extendingdistally from the proximal segment 50, the pivot member 60 configured tobe received within a proximal recess 64 formed in the proximal end 62 ofthe middle segment 52, as described below.

The middle segment 52 is pivotally connected to both the proximalsegment 50 and the distal segment 54. The middle segment 52 has aproximal end 62 including a proximal recess 64 configured to receive thepivot member 60 of the proximal segment 50. A pin 66 extends through theproximal end 62 and pivot member 60 and provides an axis about which themiddle segment 52 pivots relative to the proximal segment 50. The middlesegment 52 further includes a proximal friction recess 68 extending fromthe proximal recess 64 and configured to house a proximal frictionelement 70 and spring 72. The proximal friction element 70 and spring 72interact in such a way that the spring 72 exerts a force on the proximalfriction element 70 that in turn exerts a frictional force on the pivotmember 60. Thus, the proximal friction element 70 allows movement of themiddle segment 52 relative to the proximal segment 50 in the presence ofsufficient force to overcome the friction. In the absence of such aforce, the proximal friction element 70 operates to maintain theposition of the middle segment 52 relative to the proximal segment 50.The middle segment further has a distal end 74 including a distal recess76 configured to receive the pivot member 86 of the distal segment 54. Apin 78 extends through the distal end 74 and pivot member 86 andprovides an axis about which the distal segment 54 pivots relative tothe middle segment 52. The middle segment 52 further includes a distalfriction recess 80 extending from the distal recess 76 and configured tohouse a distal friction element 82 and spring 84. The distal frictionelement 82 and spring 84 interact in such a way that the spring 84exerts a force on the distal friction element 82 that in turn exerts africtional force on the pivot member 86. Thus, the distal frictionelement 82 allows movement of the middle segment 52 relative to thedistal segment 54 in the presence of sufficient force to overcome thefriction. In the absence of such a force, the distal friction element 82operates to maintain the position of the middle segment 52 relative tothe distal segment 54.

The distal segment 54 is pivotally connected to the middle segment 52and is configured to releasably engage the right retractor blade 30. Thedistal segment 54 includes a pivot member 86 extending proximally fromthe distal segment 54, the pivot member 86 configured to be receivedwithin the distal recess 76 formed in the distal end 74 of the middlesegment 52, as described above. The distal end 88 of the distal segment54 includes a receptacle 90 configured to receive the post 190 of theright retractor blade 30. By way of example only, the receptacle 90 is asemi-cylindrical recess that is open on one side. A locking mechanism 92is provided to releasably lock the right retractor blade 30 within thereceptacle 90 during use. The locking mechanism 92 is substantiallyhoused within an inner recess 93. The locking mechanism 92 includes anengagement latch 94 and a release button 96. The engagement latch 94 isheld in place by a first pin 98 and includes a blocking element 100extending into the receptacle 90 and an engagement arm 102 extendingaway from the blocking element 100. The engagement latch 94 isconfigured to pivot about the first pin 98. A first torsion spring 104is provided to bias the engagement latch 94 such that the blockingelement 100 protrudes from the inner recess 93 and extends at leastpartially into the receptacle 90. The release button 96 is held in placeby a second pin 106 and includes a release arm 108 extending away fromthe release button 96. The release button 96 is configured to pivotabout the second pin 106. A second torsion spring 110 is provided tobias the release button 96 such that the release button 96 protrudeslaterally from the inner recess 93 and is accessible to a user. Thelocking mechanism 92 is configured in such a way that the engagement arm102 and release arm 108 are in contact with one another while thelocking mechanism 92 is in a resting state.

In use, as the post 190 of the right retractor blade 30 is advanced intothe receptacle 90, the post 190 comes into contact with the blockingelement 100. As the post 190 continues to advance, the engagement latch94 pivots about the first pin 98 such that the engagement arm 102 movesaway from the release arm 108 and the blocking element 100 retreats intothe inner recess 93, allowing the post 190 to pass into the receptacle90. As the post 190 passes beyond the blocking element 100 and into thereceptacle 90, the first torsion spring 104 causes the engagement latch94 to pivot back into position such that the blocking element 100 againextends into the receptacle 90 and the engagement arm 102 is in contactwith the release arm 108. To disengage the right retractor blade 30, theuser exerts a pressure on the release button 96, forcing it into theinner recess 93. In the process, the release button 96 pivots about thesecond pin 106, which causes the release arm 108 to move the engagementarm 102 such that the engagement latch 94 pivots about the first pin 98,which in turn causes the blocking element 100 to retreat into the innerrecess 93. With the blocking element 100 removed, the user may disengagethe right retractor blade 30 from the right arm 26.

The left arm 28 includes a proximal segment 112, a middle segment 114,and a distal segment 116. The proximal segment 112 includes an aperture118 configured to fixedly receive the second rack 24 such that thesecond rack 24 and proximal segment 112 are generally perpendicular toone another. Thus, translation of the second rack 24 in either directioncauses a corresponding movement of the left arm 28 in the samedirection. The proximal segment 112 further includes a pivot member 120extending distally from the proximal segment 112, the pivot member 120configured to be received within a proximal recess 124 formed in theproximal end 122 of the middle segment 114, as described below.

The middle segment 114 is pivotally connected to both the proximalsegment 112 and the distal segment 116. The middle segment 114 has aproximal end 122 including a proximal recess 124 configured to receivethe pivot member 120 of the proximal segment 112. A pin 126 extendsthrough the proximal end 122 and pivot member 120 and provides an axisabout which the middle segment 114 pivots relative to the proximalsegment 112. The middle segment 114 further includes a proximal frictionrecess 128 extending from the proximal recess 124 and configured tohouse a proximal friction element 130 and spring 132. The proximalfriction element 130 and spring 132 interact in such a way that thespring 132 exerts a force on the proximal friction element 130 that inturn exerts a frictional force on the pivot member 120. Thus, theproximal friction element 130 allows movement of the middle segment 114relative to the proximal segment 112 in the presence of sufficient forceto overcome the friction. In the absence of such a force, the proximalfriction element 130 operates to maintain the position of the middlesegment 114 relative to the proximal segment 112. The middle segment 114further has a distal end 134 including a distal recess 136 configured toreceive the pivot member 146 of the distal segment 116. A pin 138extends through the distal end 134 and pivot member 146 and provides anaxis about which the distal segment 116 pivots relative to the middlesegment 114. The middle segment 114 further includes a distal frictionrecess 140 extending from the distal recess 136 and configured to housea distal friction element 142 and spring 144. The distal frictionelement 142 and spring 144 interact in such a way that the spring 144exerts a force on the distal friction element 142 that in turn exerts africtional force on the pivot member 146. Thus, the distal frictionelement 142 allows movement of the middle segment 114 relative to thedistal segment 116 in the presence of sufficient force to overcome thefriction. In the absence of such a force, the distal friction element142 operates to maintain the position of the middle segment 114 relativeto the distal segment 116.

The distal segment 116 is pivotally connected to the middle segment 114and is configured to releasably engage the left retractor blade 32. Thedistal segment 116 includes a pivot member 146 extending proximally fromthe distal segment 116, the pivot member 146 configured to be receivedwithin the distal recess 136 formed in the distal end 134 of the middlesegment 114, as described above. The distal end 148 of the distalsegment 116 includes a receptacle 150 configured to receive the post 218of the left retractor blade 32. By way of example only, the receptacle150 is a semi-cylindrical recess that is open on one side. A lockingmechanism 152 is provided to releasably lock the left retractor blade 32within the receptacle 150 during use. The locking mechanism 152 issubstantially housed within an inner recess 153. The locking mechanism152 includes an engagement latch 154 and a release button 156. Theengagement latch 154 is held in place by a first pin 158 and includes ablocking element 160 extending into the receptacle 150 and an engagementarm 162 extending away from the blocking element 160. The engagementlatch 154 is configured to pivot about the first pin 158. A firsttorsion spring 164 is provided to bias the engagement latch 154 suchthat the blocking element 160 protrudes from the inner recess 153 andextends at least partially into the receptacle 150. The release button156 is held in place by a second pin 166 and includes a release arm 168extending away from the release button 156. The release button 156 isconfigured to pivot about the second pin 166. A second torsion spring170 is provided to bias the release button 156 such that the releasebutton 156 protrudes laterally from the inner recess 153 and isaccessible to a user. The locking mechanism 152 is configured in such away that the engagement arm 162 and release arm 168 are in contact withone another while the locking mechanism 152 is in a resting state.

In use, as the post 218 of the left retractor blade 32 is advanced intothe receptacle 150, the post 218 comes into contact with the blockingelement 160. As the post 218 continues to advance, the engagement latch154 pivots about the first pin 158 such that the engagement arm 162moves away from the release arm 168 and the blocking element 160retreats into the inner recess 153, allowing the post 218 to pass intothe receptacle 150. As the post 218 passes beyond the blocking element160 and into the receptacle 150, the first torsion spring 164 causes theengagement latch 154 to pivot back into position such that the blockingelement 160 again extends into the receptacle 150 and the engagement arm162 is in contact with the release arm 168. To disengage the leftretractor blade 32, the user exerts a pressure on the release button156, forcing it into the inner recess 153. In the process, the releasebutton 156 pivots about the second pin 166, which causes the release arm168 to move the engagement arm 162 such that the engagement latch 154pivots about the first pin 158, which in turn causes the blockingelement 160 to retreat into the inner recess 153. With the blockingelement 160 removed, the user may disengage the left retractor blade 32from the left arm 28.

FIGS. 6-11 illustrate an example of a right retractor blade 30configured for use with the tissue retractor 10 described above,according to one embodiment. The right retractor blade 30 has a bladeportion 172 and a connector 174. The blade portion 172 has an interiorface 176 and an exterior face 178. The exterior face 178 is generallysmooth and rests against the soft tissue during use. The retractor blade30 is configured to rotate such that the blade 30 can self-align againstthe tissue, or in other words, find the best natural position againstthe tissue in order to reduce pressure points. The interior face 176includes a light guide 180. The light source 181 (FIG. 1) slides downthe light guide 180 to illuminate the surgical target site. The lightsource 181 may be a bundle of fiber optic cable designed to engage thelight guide 180. The light source 181 may also be bendable such that itcan be bent out of the surgeon's way as it exits the operative corridor.The light source 181 may be engaged to the retractor blade 30 prior toinserting the blade 30. The distal end 182 of the right retractor blade30 may be angled away from the interior face 176 as shown in FIGS. 10and 11 or be oriented in a straight in line with the rest of the blade30. The distal end 182 may be smooth or toothed (as shown by way ofexample in FIGS. 6-11). The distal end 182 of the blade 30 may also havetwo outer lobes 184 with a center recess 186 between the outer lobes184. This configuration allows the right retractor blade 30 to betterconform to the patient's bone structure.

The right retractor blade 30 includes a connector 174 for connecting theblade 30 to the right arm 26. The connector 174 has a head 188 and apost 190. The head 188 includes a top surface 192, a recess 194 formedwithin the top surface 192, a beveled surface 196, and an aperture 198formed within the beveled surface 196. The recess 194 is generallyoblong in shape and is configured to receive the engagement post 272 onthe engagement head 266 of the attachment handle 260. The beveledsurface 196 is configured to abut against the engagement head 266 of theattachment handle 260, and the aperture 198 is configured to receive thedistal tip 276 of the inner shaft 274 of the attachment handle 260,described in further detail in relation to FIGS. 24-27. The head 188 andpost 190 are each configured to allow connection of the blade 30 to twoinstruments at the same time (for example an attachment handle 260 andright arm 26, or attachment handle 260 and articulating arm). Thissimplifies insertion of the retractor blade 30. It also allows thesurgeon to manually retract and position the blade 30 precisely, adjustthe access driver body 20 to match the blade(s), and thereafter attachthe access driver body 20 to hold the blade(s) in position. According toa preferred usage, for example, the right retractor blade 30 is attachedto the attachment handle 260 via the head 188 and advanced to thesurgical site. The right retractor blade 30 is retracted into thedesired position and then the right arm 26 is connected to the post 190as described above. The right arm 26 is locked, fixing the position ofthe blade 30 (it is also possible to insert the blade 30 having theright arm 26 attached to the blade 30, adjust the position of the blade,and then lock the right arm 26 to hold the blade 30 in the desiredposition prior to attaching the retractor body). The attachment handle260 is then removed from the head 188.

The right retractor blade 30 is designed to rotate within the receptacle90 in order to self align in the best possible position against thepatient's soft tissue. The connector 174 is fixed relative to the blade30. The ability for the blade 30 to rotate relative to the retractor 10derives from the connection between the post 190 and the receptacle 90of the right arm 26. The post 190 can rotate freely 360 degrees withinthe receptacle 90.

FIGS. 12-17 illustrate an example of a left retractor blade 32configured for use with the tissue retractor 10 described above,according to one embodiment. The left retractor blade 32 has a bladeportion 216 and a connector 218. The blade portion 216 has an interiorface 212 and an exterior face 214. The exterior face 214 is generallysmooth and rests against the soft tissue during use. The left retractorblade 32 is configured to rotate such that the blade 32 can self-alignagainst the tissue, or in other words, find the best natural positionagainst the tissue in order to reduce pressure points. The interior face212 includes a light guide 216. The light source 201 (FIG. 1) slidesdown the light guide 216 to illuminate the surgical target site. Thelight source 201 may be a bundle of fiber optic cable designed to engagethe light guide 216. The light source 201 may also be bendable such thatit can be bent out of the surgeon's way as it exits the operativecorridor. The light source 201 may be engaged to the retractor blade 32prior to inserting the blade 32. The distal end 218 of the leftretractor blade 32 may be angled away from the interior face 212 asshown in FIGS. 16 and 17 or be oriented in a straight in line with therest of the blade 32. The distal end 218 may be smooth or toothed (asshown by way of example in FIGS. 12-17). The distal end 218 of the blade32 may also have two outer lobes 212 with a center recess 214 betweenthe outer lobes 212. This configuration allows the left retractor blade32 to better conform to the patient's bone structure.

The left retractor blade 32 includes a connector 218 for connecting theblade 32 to the left arm 28. The connector 218 has a head 216 and a post218. The head 216 includes a top surface 220, a recess 222 formed withinthe top surface 220, a beveled surface 224, and an aperture 226 formedwithin the beveled surface 224. The recess 222 is generally oblong inshape and is configured to receive the engagement post 272 on theengagement head 266 of the attachment handle 260. The beveled surface224 is configured to abut against the engagement head 266 of theattachment handle 260, and the aperture 226 is configured to receive thedistal tip 276 of the inner shaft 274 of the attachment handle 260,described in further detail in relation to FIGS. 24-27. The head 188 andpost 190 are each configured to allow each of which are configured toallow connection of the blade 32 to two instruments at the same time(for example an attachment handle 260 and left arm 28, or attachmenthandle 260 and articulating arm). This simplifies insertion of theretractor blade 32. It also allows the surgeon to manually retract andposition the blade 32 precisely, adjust the access driver body 20 tomatch the blade(s), and thereafter attach the access driver body 20 tohold the blade(s) in position. According to a preferred usage, forexample, the left retractor blade 32 is attached to the attachmenthandle 260 via the head 216 and advanced to the surgical site. The leftretractor blade 32 is retracted into the desired position and then theleft arm 28 is connected to the post 218 as described above. The leftarm 28 is locked, fixing the position of the blade 32 (it is alsopossible to insert the blade 32 having the left arm 28 attached to theblade 32, adjust the position of the blade, and then lock the left arm28 to hold the blade 32 in the desired position prior to attaching theretractor body). The attachment handle 260 is then removed from the head216.

The left retractor blade 32 is designed to rotate within the receptacle150 in order to self align in the best possible position against thepatient's soft tissue. The connector 218 is fixed relative to the blade32. The ability for the blade 32 to rotate relative to the retractor 10derives from the connection between the post 218 and the receptacle 150of the left arm 28. The post 218 can rotate freely 360 degrees withinthe receptacle 150.

As can be appreciated in the figures, the right and left retractorblades 30, 32 each have an asymmetric shape and are therefore notinterchangeable, although for example they may be mirror images of oneanother. The asymmetric shape is advantageous in that it allows forgreater conformity to the patient's anatomical structures while alsoimproving the surgical exposure, creating more space and less tissuecreep for the surgeon.

FIGS. 18-23 illustrate an example of a narrow right retractor blade 228configured for use with the tissue retractor 10 described above,according to one embodiment. Although shown and described by way ofexample in relation to a right blade 228 only, it should be understoodthat a narrow left retractor blade may be provided in a similar mannerwithout departing from the scope of the disclosure. The narrow rightretractor blade 228 may be used as an initial blade to establish theminimally invasive operative corridor to the surgical target site. Oncethe corridor has been established, the narrow right retractor blade 228may be disengaged from the right arm 26 and replaced with a right blade30. The right blade 30 (and left blade 32) has a wider distal portion tohelp keep more tissue from invading the operative corridor.

The narrow right retractor blade 228 has a blade portion 230 and aconnector 232. The blade portion 230 has an interior face 234 and anexterior face 236. The exterior face 236 is generally smooth and restsagainst the soft tissue during use. The narrow right retractor blade 228is configured to rotate such that the blade 228 can self-align againstthe tissue, or in other words, find the best natural position againstthe tissue in order to reduce pressure points. The interior face 234includes a light guide 238. The light source (not shown) slides down thelight guide 238 to illuminate the surgical target site. The light sourcemay be a bundle of fiber optic cable designed to engage the light guide238. The light source may also be bendable such that it can be bent outof the surgeon's way as it exits the operative corridor. The lightsource may be engaged to the narrow right retractor blade 228 prior toinserting the blade 228. The distal end 240 of the narrow rightretractor blade 228 may be angled away from the interior face 234 asshown in FIGS. 22 and 23 or be oriented in a straight in line with therest of the blade 228. The distal end 240 may be smooth or toothed (asshown by way of example in FIGS. 18-23). The distal end 240 of the blade228 may also have two outer lobes 242 with a center recess 244 betweenthe outer lobes 242. This configuration allows the narrow rightretractor blade 228 to better conform to the patient's bone structure.

The narrow right retractor blade 228 includes a connector 232 forconnecting the blade 228 to the right arm 26. The connector 232 has ahead 246 and a post 248. The head 246 includes a top surface 250, arecess 252 formed within the top surface 250, a beveled surface 254, andan aperture 256 formed within the beveled surface 254. The recess 252 isgenerally oblong in shape and is configured to receive the engagementpost 272 on the engagement head 266 of the attachment handle 260. Thebeveled surface 254 is configured to abut against the engagement head266 of the attachment handle 260, and the aperture 256 is configured toreceive the distal tip 276 of the inner shaft 274 of the attachmenthandle 260, described in further detail in relation to FIGS. 24-27. Thehead 246 and post 248 are each configured to allow connection of theblade 228 to two instruments at the same time (for example an attachmenthandle 260 and right arm 26, or attachment handle 260 and articulatingarm). This simplifies insertion of the retractor blade 228. It alsoallows the surgeon to manually retract and position the blade 228precisely, adjust the access driver body 20 to match the blade(s), andthereafter attach the access driver body 20 to hold the blade(s) inposition. According to a preferred usage, for example, the narrow rightretractor blade 228 is attached to the attachment handle 260 via thehead 246 and advanced to the surgical site. The narrow right retractorblade 228 is retracted into the desired position and then the right arm26 is connected to the post 248 as described above. The right arm 26 islocked, fixing the position of the blade 228 (it is also possible toinsert the blade 228 having the right arm 26 attached to the blade 228,adjust the position of the blade, and then lock the right arm 26 to holdthe blade 228 in the desired position prior to attaching the retractorbody). The attachment handle 260 is then removed from the head 246.

The narrow right retractor blade 228 is designed to rotate within thereceptacle 90 in order to self align in the best possible positionagainst the patient's soft tissue. The connector 232 is fixed relativeto the blade 228. The ability for the blade 228 to rotate relative tothe retractor 10 derives from the connection between the post 248 andthe receptacle 90 of the right arm 26. The post 248 can rotate freely360 degrees within the receptacle 90.

FIGS. 24-27 illustrate one example of an attachment handle 260configured for use with the tissue retractor 10 described above,according to one embodiment. The attachment handle 260 is shown by wayof example (FIGS. 25-27) as engaged with a right retractor blade 30however the attachment handle 260 may be engaged with any of theretractor blades shown and described herein. The attachment handle 260includes a grip 262, an elongated outer shaft 264, and an engagementhead 266 positioned at the distal end of the outer shaft 264. Theengagement head 266 includes a first abutment surface 268 and a secondabutment surface 270. A generally oblong engagement post 272 extendsgenerally perpendicularly from the first abutment surface 268. An innershaft 274 extends through the outer shaft and has a distal tip 276 thatis configured to couple with the aperture 198 of the blade 30. Theattachment handle 260 further includes a spring 278 that exerts a forceon the inner shaft 274 to bias the inner shaft 274 in a distaldirection. The proximal end of the inner shaft 274 is attached to arelease button 280.

When the attachment handle is coupled with the blade 30, the firstabutment surface 268 abuts the top surface 192 of the head 188 of theblade 30. The second abutment surface 270 abuts the beveled surface 196of the blade 30. The engagement post 272 is inserted into the recess 194of the blade 30, and the distal tip 276 of the inner shaft 274 isreceived within the aperture 198 of the blade 30. The distal biasing ofthe inner shaft 274 keeps the distal tip 276 engaged with the aperture198 of the blade 30, effectively locking the attachment handle 260 tothe blade 30. To disengage, the use pulls back on the release button,which pulls the distal tip 276 of the inner shaft 274 out of theaperture 198 and allows for decoupling of the blade 30 and attachmenthandle 260.

The various features described herein provide functional benefits duringspine surgery. For example, the dual pivots enable adjustment of thearms 26, 28 such that the height of the distal segments may be adjustedwhile allowing the distal segments to remain parallel to the patient'sbody. Thus the angle of the retractor blades will remain relativelyconstant. The friction elements described herein operate to easily allowthis adjustment to occur, but also to maintain the desired adjustmentwithout requiring additional hands, tools, or time. The locking elementis operable to allow a snap-fit engagement between the retractor bladesand the retractor arms without any other manipulation required by theuser. Furthermore, the locking element is disengaged by depressing asingle button allowing for the removal of the retractor blades.

FIGS. 28-30 illustrate an example of a bone anchor 282 configured foruse with the tissue retractor 10 during a medialized PLIF procedureaccording to one embodiment. By way of example only, the bone anchor 282includes a tulip 284 and a shank 286. The tulip 284 is configured tolockingly receive a spinal rod 16 (FIG. 1) therein. The shank 286includes a head 288, a neck 290, and a threaded region 292. The head 288and neck 290 are configured to allow for polyaxial movement of the shank286 relative to the tulip 284. By way of example only, the shank 286comprises three different thread zones. The first thread zone 294 isconfigured to provide strong purchase in cortical bone. Cortical bone isprevalent at the posterior margin of the pedicle and is especially densein the area surrounding the articulating surfaces of the facet wherethread zone one will reside when fully inserted. The second thread zone296 is configured to provide strong purchase through the pedicle wherethe cortical bone is less dense than the outer periphery cortical bone.The third thread zone 298 is configured to provide strong purchase incortical bone. Cortical bone is prevalent at the anterio-lateral marginof the vertebral body within the ring apophysis in which the thirdthread zone 298 will reside when fully inserted. Third thread zone 298is also configured to advance through the bone without creating voidswithin bone that would potentially reduce purchase of the first and/orsecond thread zones 294, 296, respectively. This is accomplished byproviding a taper on the distal tip of the shank and on the second leadsuch that the second lead does not violate the minor diameter of thesecond thread zone 296 or the first thread zone 294.

FIGS. 31-38 illustrate an example of an interbody implant 300 configuredfor use with the tissue retractor 10 during a medialized PLIF procedureaccording to one embodiment. The interbody implant 300 includes aleading end 302, a trailing end 304, a pair of opposing vertebralcontact surfaces 306, a first side 308, a second side 310, and a fusionaperture 312. The leading end 302 is tapered such that the implant 300is capable of being impacted into an intervertebral disc space. Thetrailing end 304 includes an aperture 314 configured to engage aninsertion tool (not shown). By way of example only, the aperture 314 isthreaded, however other configurations are possible. The first side 308includes an elongated recess 316 extending substantially the length ofthe first side 308 and intersecting with the trailing end 304. Theelongated recess 316 is dimensioned to receive a stability prong of aninsertion tool (not shown). The implant is configured specifically forfar lateral positioning within the disc space. For example, the secondside 310 is contoured to complement the lateral aspects of a vertebralbody such that the implant may be positioned along the lateral edge andrests upon the dense cortical bone of the apophyseal ring along thelateral edge. As pictured in FIG. 47, an implant 300 is preferablypositioned far laterally on each side of the disc space (e.g.bilaterally). This bilateral placement along the apophyseal ring on eachlateral edge of the disc space provides structural advantage overtypical bilateral PLIF implant positioning which does not extend out allthe way to the lateral edges. The opposing contact surfaces 306 areconfigured such that either surface can be oriented to contact the uppervertebral body. Thus the implant 300 is reversible, or in other words, asingle implant configuration can be utilized as either the left implantor right implant (when positioned bilaterally as preferred).

The implant 300 is configured to be inserted via straight impaction oran insert and rotate technique in which the implant is inserted on itsside and then rotated into position inside the intervertebral space. Tofacilitate the insert and rotate technique for example, the first andsecond sides 308, 310 include smooth surfaces that taper toward theleading end 302. This allows for easier insertion into the disc space.The vertebral contact surfaces 306 may include anti-migration features318 to prevent the implant 300 from migrating once it is positioned inthe desired place in the intervertebral space. That is, the implant 300is inserted with the first and second sides 308, 310 initially incontact with the vertebral endplates during insertion. Thereafter, theimplant 300 is rotated 90° such that the vertebral contact surfaces 306and specifically the anti-migration features 318 are brought intocontact with the endplates. In this second orientation the implant 300is also taller near the leading end 302 in order to accommodate thelordotic curvature of the lumbar spine. The fusion aperture 312 extendsthrough the implant 300 between the vertebral contact surfaces 306 andis configured to receive fusion-promoting material. The implant 300 alsoincludes a first radiographic marker 320 positioned near the leading end302 and a second radiographic marker 322 positioned near the trailingend 304. The radiographic markers 320, 322 may be composed of anymaterial suitable for viewing under fluoroscopy, for example includingbut not limited to titanium and other metals.

Traditional PLIF exposure requires exposure out to transverse process.Exposure includes stripping of musculature and associated morbidity.Screws are advanced into the vertebral body through the pedicle startingat the intersection of the transverse process and the inferiorarticulating process of the superior facet. Typical trajectories betweenpedicle screws within the same vertebral body converge. The trajectoryis also often directed inferiorly.

The present application describes a medialized PLIF exposure. Themedialized exposure can be made much smaller than the traditionalexposure. Exposure does not require stripping of musculature all the wayout to the transverse process. Exposure generally opens out only to thefacet joints on the lateral margin. Screws are still advanced into thevertebral body through the pedicle, however, the starting point is moremedial and slightly inferior. The starting point is typically justmedial and inferior to the articulating surface of the superior facet.

FIGS. 39-48 illustrate various steps in the method of performing aminimally invasive PLIF procedure using the tissue retractor 10, boneanchors 282, and implants 300, described herein according to one exampleembodiment. Referring first to FIG. 39, after the affected spinal levelis identified, an incision is made exposing the spinal elements. Thenarrow retractor blade 228 is used first (both right and left blades.The narrow retractor blades are attached to the attachment handles 260in the manner described above. The narrow retractor blades 228 may beused to retract the patient's tissue only until the blades arepositioned directly over the facet capsule, with the center recess 244resting on the facet bone (for example as shown in FIG. 40). In thismanner the left and right retractor blades not only hold tissue out ofthe operative corridor but they also geographically define the exposuresuch that the blades essentially provide anatomy landmarks easilyorienting the surgeon to anatomy within the exposure. While manuallyholding the exposure using the attachment handles 260, the right andleft arms 26, 28 of the tissue retractor 10 may be attached to the rightand left blades in the manner described above. The tissue retractor 10is oriented so the access driver body 20 is placed cephalad of theexposure (FIG. 40). At this point, the tissue retractor 10 may beattached to an articulating arm in order to immobilize the retractor 10relative to the operating table. Once the tissue retractor 10 has beenattached to the articulating arm, the narrow retractor blades 228 may bereplaced with the right and left wide retractor blades 30, 32 asdesired. Alternatively, the right and left wide retractor blades 30, 32may be used from the beginning of the procedure, or alternatively stillthe narrow retractor blades 228 may be used throughout the entireprocedure. Light cables 181 may be introduced into the exposure byengaging the light guides 180 as described above.

The next step is to identify the proper trajectory for the bone anchors12. FIGS. 41-44 illustrate the proper placement and trajectory of thebone anchors 12. FIG. 41 illustrates a spinal column with typicalmedialized trajectories T₁-T₄ as they are on multiple vertebral levels.Typical trajectories between medialized pedicle screws within the samevertebral body diverge and are also often directed slightly superiorly.Inserting screws along this trajectory generally allows for placement ofa shorter screw shank than those placed along traditional PLIFtrajectories because the medialized trajectory takes advantage of theanatomical location of cortical bone within the vertebral body. Corticalbone provides greater purchase to screws because it has a higher densityas compared to cancellous bone. FIGS. 43-44 illustrate an example ofthree different spots 1, 2, 3 where the medialized trajectory T₁ takesadvantage of the cortical bone. The cortical bone is located about theperiphery of the vertebral body 3 and the periphery of the posteriorelements including the pedicle 2. Once the proper location andtrajectory has been determined, pilot holes P₁-P₃ (FIG. 42) are formedin the bone and the bone anchors 12 may be implanted. According to oneexample embodiment (and illustrated in FIG. 45), the shanks 286 may beimplanted first and then the tulips 284 may be subsequently added nearthe end of the procedure. This allows for more space within the surgicalexposure to operate on the spine (e.g. removing bone and disc material,positioning implants, etc. . . . ) as there is less hardware presentduring the procedure.

Once the shanks 286 have been implanted, the surgeon may perform abilateral decompression by removing the inferior articular processes andsuperior ⅔ of the superior articular processes. A discectomy may then beperformed in a conventional manner. After determining the appropriatesized interbody implants 300, the implants 300 are inserted into thedisc space in the manner described above, using the insert and rotatetechnique (FIG. 46). By way of example, two interbody implants 300 maybe implanted in the disc space, one on the contralateral side and one onthe ipsilateral side. Proper placement of the implants 300 is shown inFIG. 47. Once the implants 300 are properly inserted, the tulips 284 maybe added to the shanks 286 and the spinal rods 16 may be added,completing the construct (FIG. 48).

While the inventive features described herein have been described interms of a preferred embodiment for achieving the objectives, it will beappreciated by those skilled in the art that variations may beaccomplished in view of these teachings without deviating from thespirit or scope of the invention.

1. (canceled)
 2. A method comprising: providing a first retractor bladebeing asymmetric about a first retractor blade longitudinal axis andhaving a first retractor blade recess defining, in part, two firstretractor blade lobes on opposite sides of the first retractor bladelongitudinal axis; and providing a second retractor blade beingasymmetric about a second retractor blade longitudinal axis and having asecond retractor blade recess defining, in part, two second retractorblade lobes on opposite sides of the second retractor blade longitudinalaxis; exposing a surgical site that includes a first facet tissue regionand a second facet tissue region; resting the first retractor bladerecess at the first facet tissue region; and resting the secondretractor blade recess at the second facet tissue region.
 3. The methodof claim 2, wherein the two first retractor blade lobes include a largerfirst retractor blade lobe that is larger than a smaller first retractorblade lobe; and wherein the two second retractor blade lobes include alarger second retractor blade lobe that is larger than a smaller secondretractor blade lobe.
 4. The method of claim 3, wherein resting thefirst and second recesses at the first and second facet tissue regionsincludes: resting the first and second recesses such that: the largerfirst retractor blade lobe is more cephalad than the smaller firstretractor blade lobe the larger second retractor blade lobe is morecephalad than the smaller second retractor blade lobe.
 5. The method ofclaim 2, further comprising: before resting the first and secondrecesses at the first and second facet tissue regions: coupling thefirst retractor blade to a first handle; and coupling the secondretractor blade to a second handle.
 6. The method of claim 5, furthercomprising: after resting the first and second recesses at the first andsecond facet tissue regions: decoupling the first retractor blade fromthe first handle; decoupling the second retractor blade from the secondhandle; attaching the first retractor blade to a first arm of a tissueretractor; and attaching the second retractor blade to a second arm ofthe tissue retractor.
 7. The method of claim 6, further comprising:disposing the tissue retractor at a location cephalad of the exposedsurgical site.
 8. The method of claim 7, further comprising: couplingthe tissue retractor to an articulating arm while the tissue retractoris cephalad of the exposed surgical site.
 9. A method comprising:providing a first left retractor blade being asymmetric about a firstleft retractor blade longitudinal axis and having a first left retractorblade recess defining, in part, two first left retractor blade lobes onopposite sides of the first left retractor blade longitudinal axis;providing a first right retractor blade being asymmetric about a firstright retractor blade longitudinal axis and having a first rightretractor blade recess defining, in part, two first right retractorblade lobes on opposite sides of the first right retractor bladelongitudinal axis; forming an incision; inserting the first leftretractor blade into the incision; inserting the first right retractorblade into the incision; and after inserting the first left and rightretractor blades, retracting tissue with the first left and rightretractor blades such that the first left and right retractor blades arepositioned proximate a facet capsule.
 10. The method of claim 9, furthercomprising: resting the first left retractor blade recess at a lefttissue region proximate the facet capsule; and resting the first rightretractor blade recess at a right tissue region proximate the facetcapsule.
 11. The method of claim 9, further comprising: before insertingthe first left and right retractor blades into the incision: couplingthe first left retractor blade to a first handle; and coupling the firstright retractor blade to a second handle.
 12. The method of claim 11,further comprising: manually holding the retraction using the firsthandle and the second handle.
 13. The method of claim 12, furthercomprising: providing a tissue retractor having a left arm and a rightarm; and while manually holding the retraction using the first handleand the second handle: attaching the first left retractor blade to theleft arm; and attaching the first right retractor blade to the rightarm.
 14. The method of claim 13, further comprising: orienting thetissue retractor such that a driver body of the tissue retractor isplaced cephalad of the incision.
 15. The method of claim 14, furthercomprising: attaching an articulating arm to the tissue retractor. 16.The method of claim 15, further comprising: after attaching thearticulating arm to the tissue retractor: replacing the first leftretractor blade with a second left retractor blade; and replacing thefirst right retractor blade with a second right retractor blade.
 17. Themethod of claim 16, wherein: the second left retractor blade is widerthan the first left retractor blade; and the second right retractorblade is wider than the first right retractor blade.
 18. The method ofclaim 16, further comprising: performing at least a portion of aposterior lumbar interbody fusion through an opening formed between thesecond left and right retractor blades.
 19. A method comprising:providing a retractor body that includes: a first arm having a first armreceptacle having a first side opening; and a second arm having a secondarm receptacle having a second side opening; inserting a first retractorblade connector of a first retractor blade into the first side, whereinthe first retractor blade includes: a first longitudinal axis extendingthrough a first proximal end and a first distal end and passing througha midpoint of a first maximum width, a first outer lobe situated on oneside of the first longitudinal axis; a second outer lobe situated on theopposite side of the first longitudinal axis from the first outer lobe;and a first recess separating the first outer lobe and the second outerlobe; inserting a second retractor blade connector of a second retractorblade into the second side, wherein the second retractor blade includes:a second longitudinal axis extending through a second proximal end and asecond distal end and passing through a midpoint of a second maximumwidth; a third outer lobe situated on one side of the secondlongitudinal axis; a fourth outer lobe situated on the opposite side ofthe second longitudinal axis from the third outer lobe; and a secondrecess separating the third outer lobe and the fourth outer lobe. 20.The method of claim 19, further comprising: forming an incision;inserting the first retractor blade into the incision; inserting thesecond retractor blade into the incision; and retracting tissue with theinserted first left and right retractor blades by operating theretractor body.
 21. The method of claim 19, further comprising:releasing the first retractor blade by actuating a first blade releasemechanism associated with the first side opening; and releasing thesecond retractor blade by actuating a second blade release mechanismassociated with the second side opening.